[css-font-loading] Add note about removing SetClass. Fix IDL around promises.

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extra : rebase_source : 855f21c6be35c810b24d58b5cf069468e81592d6
[css-align] Some minor cleanup of baseline stuff.

--HG--
extra : rebase_source : 056d2d397b85e23130968672ff974f1da551c869